I'm a geochemist. In the past ten years I've fixed mass spectrometers, blasted sapphires with a laser beam, explored for uranium in a nature reserve, and measured growth patterns in fish ears, and helped design the next generation of the world's most advanced ion probe. My main interest is in-situ mass spectrometry, but I have a soft spot in my heart for thermodynamics, drillers, and cosmochemistry.

Thursday, August 06, 2015

There has been a bit in the science press about the newly
discovered exoplanet, Kepler 452b. This related to the observation that it is
in the “habitable zone” of a sun-like star.
The big news, as always, is that this planet is completely unlike
anything in our solar system. If it is solid, it has three times the mass than
every rocky body in our solar system combined. If it is not solid, then it is
one of the sub-neptune planets common everywhere but around our star. But there are two points in particular which
have been ignored- or at least not appreciated, which I would like to expound
on.

Firstly, we can see them, but they can’t see us. There are two main techniques used for
detecting planets around stars: Radial velocity, and transits. The motion of the planet around the star
pulls the star backwards and forwards, in proportion to their relative masses.

With the radial velocity method measures the very small
Doppler shift in the light of the star created by this pull. However, in order
to see this motion, the orbit of the planet around the star needs to be
somewhat edge-on as seen from earth. If we are looking town down on the orbit,
then the star doesn’t move towards or away from us; it just goes in a circle
(or ellipse). And sideways motion in the sky is much harder to detect that
motion towards of away from Earth.

With transit detection, the crossing of the planet across
the face of the star (as seen from Earth) causes the light from the start to
dim a little bit in a periodic fashion. This requires Earthly observers to be
in the same plane as the orbit of the planet- For a Earth-like planet orbiting
a sun-like star, the planet will only transit if the Earth is within a half
degree of the planet’s orbital plane.
The Kepler mission is a transit mission; all the planets it detects are
systems which are edge-on as seen from Earth.

For aliens trying to detect us using the transit method,
they need to be viewing us from a star that lies in the ecliptic. Basically, if
they want to see the Earth pass in front of the sun, to detect its transit,
then from our point of view, the sun needs to cross in front of their star.

However, the Kepler primary mission* field of view is nowhere
near the ecliptic. It is, fore the most part, more than 60 degrees from the
ecliptic. This makes transit detection of the Earth in front of the sun
impossible from any star systems in the original Kepler field of view. And due
to the high angle, radial velocity measurements of the Earth’s pull on the sun
will be less than half as effective as our radial velocity measurements of
their planets.

So the Kepler mission isn’t just a telescope. It is a spy satellite, peering down on a
thousand planets circling hundreds of distance star, all of whom are blissfully
unaware of our planet’s existence. If
there are aliens on Kepler 452b- or any other planet Kepler discovers, they
aren’t waving at us, because assuming technological parity, they can’t possibly
know that we are here.

Of course, we know that they are there. And it might be that one day,. given a modest
technological advancement, someone could sent a colony ship on a hundred
thousand year mission to visit them.
However, the visit could easily overstay its welcome.

Kepler 452b is probably not an Earthlike planet. However, if
it does have an Earthlike composition, then it is a gigantic hunk of rock and
metal three times more massive than every rocky-metal planet in our solar system
combined. Due to gravitational self-compression, this planet would have a mass
six times that of Earth. At 36
hellagrams, it is just under half the mass of Uranus. The surface gravity would
be a crushing 2.3 times greater than on Earth.
No rocket we currently have could even leave the launch pad under suck
crashing gravity. And even if it did,
the velocity required to achieve orbital velocity, 15.5 km/s, is almost twice
what is required on Earth.

Although technology is sure to advance if we are to get the
ability to launch colony ships, such a huge planet would trap any rocket
conceivable with current technology.
Kepler 452b is, in essence, a gigantic Hotel California, from which
no-one can ever leave. As a result, any
short-lived visitation attempt would inevitably become a permanent stay.

So don’t be too disappointed if the locals on Kepler 452b
don’t wave back. They are blissfully
unaware that we are staring at them. And
if they did know, the fact that we would wear out our welcome upon visiting by
a factor of infinity is unlikely to cheer them up.

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Disclaimer:

All opinions, measurements, figures, and facts on this page are the personal opinions of Charles W. Magee, Jr, and do not represent the views of any of his employers: past, present, present-but-about-to-be-past, or future. None of the content herein has been subject to peer review, and should be treated with caution or derision. Any passing mention of OSHA code violations, criminal activities, unethical or unscientific behavior, or the clandestine Australian nuclear weapons program are fictions created to make rhetorical points, and do not represent the reality of my, or anyone else's, workplace. Do not attempt any scientific protocols described herein at home, with the exception of the chocolate chip cookie recipe. Do not apply the products of that protocol to individuals with heart disease, diabetes, high blood pressure or cholesterol, egg, wheat, dairy, or chocolate allergies. Do not view this blog continuously for more than 45 minutes without stretching and taking other precautions to prevent computer-related chronic injury.

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